1. Field of the Invention
The present invention is directed to turbine housings and a method of forming a turbine housing and, in particular, to a turbine housing and a method for forming the turbine housing in which the housing is formed from a plurality of members and the air turbulence at the mating portions of the members is reduced by offsetting the mating wall portions of one of the members with respect to those of the other member. The mating portions are offset with respect to one another such that air flowing in the turbine housing formed by the wall members does not see the edge of the mating wall portions of the second member in the direction of flow.
The term "flow" as used herein is used to describe the path and movement of the working fluid from the turbine inlet to the turbine housing exit. Obstructions to flow are of particular importance due to the frictional resistance put on the turbine rotor when this field of rotating fluid is impeded. The fluid can be thought of as rotating with the turbine rotor in planes of equal thickness, the planes closer to the turbine rotor having more frictional bond to the turbine rotor than the planes further from the turbine rotor. Because of friction between the planes and with the turbine rotor, obstruction to the movement of a plane close to the turbine rotor is particularly detrimental. Hence, the problem of obstructions in the path of the fluid flow is most critical when the turbine housing is designed to be minimized because obstructions in the housing walls are close to the turbine rotor.
2. Description of the Prior Art
In prior art turbine housings, the housings are formed by placing together a plurality of housing sections or mating members. These housing sections or mating members are joined together at mating wall portions. A single unitary housing is not formed because of the difficulty in manufacturing. For example, in small air turbines which are made of molded plastic, it would be extremely difficult to form a mold which could produce a unitary housing. Thus, in a commercial environment, it has become necessary to form a plurality of sections and then fasten or fix these sections together.
In the manufacture of housing sections, it is standard practice to design the distance between opposite walls of each of the housing sections to be equal. Further, in the peripheral wall of the housing, which is usually circular, the same radius is used for each of the housing sections.
As a practical matter, the distance between opposite walls and the radius have a certain tolerance and, in some situations, the distance between opposite walls is less than the designed distance and, in some cases, it is greater than the designed distance. Because of this variation in distance, when two adjacent housing sections are placed together, if the distance between opposite walls at the mating portions of a succeeding section in the direction of flow is less than the distance between opposite walls at the mating portions of the preceding section, then air flowing in the turbine will see the edges of the mating surface of the succeeding housing section which project into the housing which forms the turbine chamber. These projections will create air turbulence. Furthermore, the air turbulence created by the projections will itself create additional air turbulence which will extend further into the housing. This air turbulence reduces the efficiency of the turbine.